Doing DMX512 on most micros require you to count cycles carefully and to pull a few tricks to get the speed up - use alternate register bank to save interrupt variables, locate the receive buffer on a address starting at 0xzz00 so you only have to test the hi byte of the pointer etc. There's not much time for error checking.

FYI. Finding the right high frequency crystals and getting them to oscillate at the right frequency is always a pain - search out some old 286/386 motherboards and you may find a 32mhz oscillator module - rip it out,give it 5 volts and you'll have 32mhz without the pain.